"True redtails" are BCC boas (Surinames, Peruvians, Guyanas, etc), so when someone says they have a Colombian (It's with an "o" not a "u") red tail boa it's not totally correct IMO but a lot of people call all boas "red tails" anyway. Sometimes you can tell certain characteristics if a BCI is crossed with a BCC (possible redder tail, saddles, face markings, etc) but for locals the only true way of telling is knowing the snake's origins (and some Colombians may have peaked saddles and whatnot like a BCC would while some BCC boas don't have much peaking). Hog Island Boas are BCI and not a Colombians or a BCC, they are usually lighter colored with lots or minimal peppering with more orange tails.
Check out this site for lots of good info: http://www.riobravoreptiles.com/index.htm